During the interview, when asked what word came to mind regarding Mrs O'Neill, Mrs Foster said: "I am not going to be sexist because I can't..." but when pushed by journalist Niamh Horan, she responded: "Blonde!".

When asked to expand she said: "Michelle is very attractive. She presents herself very well and she always is - you know - her appearance is always very 'the same'.

"You never see her without her make-up. You never see her without her hair [looking] 'perfect'."

In the same interview, Mrs Foster criticised scrutiny of her own appearance when the RHI scandal erupted last year.

She said: "Nobody looking at my Twitter feed or social media could say that there wasn't misogyny."

She described the "onslaught" as "horrific" and said the comments had physically upset her 17-year-old daughter.

Sinn Féin MLA Elisha MCallion called on Mrs Foster to retract the "sexist and disparaging remarks" about Mrs O'Neill.

"It is totally unacceptable in the 21st century for a political leader to characterise another political leader based on the colour of their hair.

"The irony of talking about sexism and misogyny appears to be totally lost on Arlene Foster when she makes such remarks about others."

The journalist who interviewed Mrs Foster defended the comments on The Nolan Show on Monday.

Niamh Horan said: "Blonde is a descriptive world, it's everyone else this morning attaching their own meaning to it."

Speaking to the BBC, the DUP's Sammy Wilson denied the comments were sexist, insisting that Arlene Foster was just stating the obvious.

He described the row as a "smokescreen" to political issues and said that Sinn Féin was trying to play the victim: "[going] out of their way to find grievance where no grievance was meant.

"If it had been me, I would have been making some far, far more derogatory comments about the way she's handled the job since she took over," he said.

Image copyright@SHAUNAREPORTS TwitterImage caption
A cartoon crocodile in a blonde-wig circulated widely on social media.

Social media has been divided as to whether the comments were another "crocodile moment" by the DUP, or an overreaction by Sinn Féin politicians and some on social media.

DUP MLA Christopher Stalford mocked the reaction on his Facebook page, insinuating Sinn Féin was being over-sensitive and referred to them as "snow flakes". He also shared a photo of his blonde children on Twitter jokingly captioned "Blondies for Arlene!".